Small Molecule-Based Promotion of PKCα-Mediated β-Catenin Degradation Suppresses the Proliferation of CRT-Positive Cancer Cells

Aberrant accumulation of intracellular β-catenin is a well recognized characteristic of several cancers, including prostate, colon, and liver cancers, and is a potential target for development of anticancer therapeutics. Here, we used cell-based small molecule screening to identify CGK062 as an inhibitor of Wnt/β-catenin signaling. CGK062 promoted protein kinase Cα (PKCα)-mediated phosphorylation of β-catenin at Ser33/Ser37, marking it for proteasomal degradation. This reduced intracellular β-catenin levels and consequently antagonized β-catenin response transcription (CRT). Pharmacological inhibition or depletion of PKCα abrogated CGK062-mediated phosphorylation and degradation of β-catenin. In addition, CGK062 repressed the expression of the genes encoding cyclin D1, c-myc, and axin-2, β-catenin target genes, and thus inhibited the growth of CRT-positive cancer cells. Furthermore, treatment of nude mice bearing PC3 xenograft tumors with CGK062 at doses of 50 mg/kg and 100 mg/kg (i.p.) significantly suppressed tumor growth. Our findings suggest that CGK062 exerts its anticancer activity by promoting PKCα-mediated β-catenin phosphorylation/degradation. Therefore, CGK062 has significant therapeutic potential for the treatment of CRT-positive cancers.